[PATCH 5.10 266/406] cpufreq: Fix the race condition while updating the transition_task of policy

Greg Kroah-Hartman
2023-09-17T19:35:23Z

From: Liao Chang <liaochang1@huawei.com>

[ Upstream commit 61bfbf7951ba561dcbdd5357702d3cbc2d447812 ]

The field 'transition_task' of policy structure is used to track the
task which is performing the frequency transition. Using this field to
print a warning once detect a case where the same task is calling
_begin() again before completing the preivous frequency transition via
the _end().

However, there is a potential race condition in _end() and _begin() APIs
while updating the field 'transition_task' of policy, the scenario is
depicted below:

Task A Task B

/* 1st freq transition */
Invoke _begin() {
...
...
}
/* 2nd freq transition */
Invoke _begin() {
... //waiting for A to
... //clear
... //transition_ongoing
... //in _end() for
... //the 1st transition
|
Change the frequency |
|
Invoke _end() { |
... |
... |
transition_ongoing = false; V
transition_ongoing = true;
transition_task = current;
transition_task = NULL;
... //A overwrites the task
... //performing the transition
... //result in error warning.
}

To fix this race condition, the transition_lock of policy structure is
now acquired before updating policy structure in _end() API. Which ensure
that only one task can update the 'transition_task' field at a time.

Link: https://lore.kernel.org/all/b3c61d8a-d52d-3136-fbf0-d1de9f1ba411@huawei.com/
Fixes: ca654dc3a93d ("cpufreq: Catch double invocations of cpufreq_freq_transition_begin/end")
Signed-off-by: Liao Chang <liaochang1@huawei.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/cpufreq/cpufreq.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 58342390966b7..5b4bca71f201d 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -450,8 +450,10 @@ void cpufreq_freq_transition_end(struct cpufreq_policy *policy,
policy->cur,
policy->cpuinfo.max_freq);

+ spin_lock(&policy->transition_lock);
policy->transition_ongoing = false;
policy->transition_task = NULL;
+ spin_unlock(&policy->transition_lock);

wake_up(&policy->transition_wait);
}
--
2.40.1